Grinding apparatus

ABSTRACT

A grinding apparatus includes a table having a holding surface, a grinding unit grinding a wafer held on the holding surface, a notification portion notifying an operator of information, an imaging unit illuminating a ground surface of the wafer which is held and ground with an illumination and imaging the ground surface, a detecting portion detecting a cross line in an imaged picture, a memory storing an X-axis and Y-axis coordinate position of an intersection point of the cross line detected, a spotlight illuminating the holding surface at the X-axis and Y-axis coordinate position stored, and a controller causing the notification portion to notify the operator that the cross line has been detected and stopping grinding operations of the grinding apparatus.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a grinding apparatus for grinding a workpiece such as a semiconductor wafer.

Description of the Related Art

In a grinding apparatus for grinding a wafer, the wafer is held under suction on a holding surface of a holding table, the holding surface being composed of a porous member, and a rotating grinding stone is positioned in parallel to the holding surface, whereby the wafer held on the holding surface is ground with a grinding surface of the rotating grinding stone. When the wafer held on the holding surface is ground with the grinding stone with a minute substance such as a grinding swarf or an abrasive grain got stuck between the holding surface of the holding table and a lower surface of the wafer, a cross-shaped crack is formed on a ground surface of the wafer directly above the minute substance. To prevent the cross-shaped crack from being formed in the wafer, the holding surface before the wafer is held under suction is cleaned with a cleaning apparatus described in Japanese Patent No. 4079289 and Japanese Patent No. 5538971 so as not to cause a cross-shaped crack to be formed in the wafer.

SUMMARY OF THE INVENTION

However, when the minute substance still remains on the holding surface having been subjected to cleaning by use of the cleaning apparatus described above, a cross-shaped crack is caused to be formed. Accordingly, before the wafer is held under suction on the holding surface of the holding table, it is required to check whether a minute substance adhered to the holding surface is present or not. In view of this, the holding surface is imaged with an imaging camera. However, it is difficult for an operator to determine whether a pattern detected on the holding surface is that of a porous ceramic constituting the holding surface or the minute substance, based on the imaged picture obtained.

To solve this problem, the grinding apparatus is configured such that, when a cross-shaped crack is detected in a ground wafer, an operator can immediately grasp a position of a holding surface of a holding table (a position where a minute substance is adhered onto the holding surface) corresponding to a position where the cross-shaped crack is formed in the wafer to remove the adhered substance from the holding surface, whereby further occurrence of a cross-shaped crack in a wafer in the subsequent wafer grinding is prevented.

It is therefore an object of the present invention to provide a grinding apparatus capable of instantly removing an adhered substance causing a cross-shaped crack from a holding surface.

In accordance with an aspect of the present invention, there is provided a grinding apparatus including a holding table including a porous plate having a holding surface on which a wafer is held, holding table rotation means rotating the holding table with a center of the holding table as an axis for rotation, grinding means grinding the wafer held on the holding surface with grinding stones, notification means notifying an operator of various kinds of information, imaging means illuminating a ground surface of the wafer which is held on the holding surface and ground with the grinding stones with an illumination and imaging the ground surface, detecting means detecting a cross line in a picture imaged by the imaging means, storage means storing an X-axis and Y-axis coordinate position of an intersection point of the cross line detected by the detecting means, a spotlight illuminating the holding surface at the X-axis and Y-axis coordinate position stored in the storage means, and control means causing the notification means to notify the operator that the detecting means has detected the cross line and stopping grinding operations of the grinding apparatus.

According to the present invention, when a cross-shaped crack is caused in the wafer which has been ground, it is possible to illuminate the holding surface directly below the cross-shaped crack with a spotlight, thereby enabling the operator to grasp immediately a position where a grinding swarf, an abrasive grain, or the like is adhered onto the holding surface after taking the wafer off from the holding surface. Then, the operator removes the minute substance adhered to the illuminated position of the holding surface, so that the minute substance causing a cross-shaped crack can be instantly removed from the holding surface.

The above and other objects, features and advantages of the present invention and the manner of realizing them will become more apparent, and the invention itself will best be understood from a study of the following description and appended claim with reference to the attached drawings showing a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view illustrating an example of a grinding apparatus;

FIG. 2 is a cross-sectional view illustrating an example of a holding table, cleaning means, and imaging means;

FIG. 3 is a cross-sectional view illustrating a state in which a ground surface of a wafer which is held on a holding surface and has been ground with grinding stones is imaged with the imaging means while being illuminated with an illumination;

FIG. 4 is a plan view illustrating the state in which the ground surface of the wafer which is held on the holding surface and has been ground with the grinding stones is imaged with the imaging means while being illuminated with the illumination; and

FIG. 5 is an explanatory view illustrating a case in which a cross line in a picture imaged by the imaging means is detected by detecting means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A grinding apparatus 1 illustrated in FIG. 1 is an apparatus for subjecting a wafer W held under suction on a holding table 30 to grinding processing. The wafer W illustrated in FIG. 1 is a circular plate-shaped semiconductor wafer composed of a silicon-based material, for example, and a front surface Wa of the wafer W facing downward in FIG. 1 has a plurality of devices formed thereon, with a protective tape T attached to the front surface Wa to be protected. A back surface Wb of the wafer W facing upward is a ground surface which is subjected to grinding processing. At an outer peripheral edge of the wafer W, a notch N as a mark for indicating crystal orientation of the wafer W is formed in such a state as to be recessed radially inward toward a center of the wafer W.

On a front side (−X direction side) of a base 10 of the grinding apparatus 1, there is disposed inputting means 19 for inputting processing conditions and the like with respect to the grinding apparatus 1 by an operator. In addition, on the front side on the base 10, there are disposed a first cassette 331 for storing the wafer W before grinding and a second cassette 332 for storing the wafer W after grinding. Between the first cassette 331 and the second cassette 332, there is disposed a robot 330 including an articulated arm which unloads the wafer W before grinding from the first cassette 331 and loads the wafer W after grinding into the second cassette 332.

In a movable region of the robot 330, there is provided a temporary setting table 333 a temporarily setting the wafer W before processing thereon, and the temporary setting table 333 a has positioning means 333 b disposed thereon. The positioning means 333 b positions (centers) the wafer W placed on the temporary setting table 333 a after being unloaded from the first cassette 331 at a predetermined position by pushing the outer peripheral edge of the wafer W with each of positioning pins which reduces a diameter.

On a lateral side of the temporary setting table 333 a, a detection portion 333 c detecting the notch N of the wafer W is disposed. The detection portion 333 c includes a reflection type optical sensor or a transmission type optical sensor, for example. When the outer periphery of the wafer W passes through a detection region (lower side) of the detection portion 333 c along with rotation of the temporary setting table 333 a holding the centered wafer W thereon, the detection portion 333 c can detect the notch N formed at the outer peripheral edge of the wafer W. Incidentally, it may be configured such that, assuming that the detection portion 333 c is constituted by a camera or the like, the detection portion 333 c image-processes a picture imaged by the camera, so that the notch N at the outer peripheral edge of the wafer W can be detected. In addition, in the movable region of the robot 330, cleaning means 334 cleaning the wafer W after grinding is disposed. The cleaning means 334 is a single wafer spinner cleaning apparatus, for example.

In a vicinity of the positioning means 333 b, first transfer means 335 is disposed, and second transfer means 336 is disposed in a vicinity of the cleaning means 334. The first transfer means 335 transfers the wafer W before grinding, which is placed on the temporary setting table 333 a to be centered, to any one of the holding tables 30 illustrated in FIG. 1, and the second transfer means 336 transfers the wafer W after grinding which is held on any one of the holding tables 30 to the cleaning means 334.

On a rear side of the first transfer means 335 on the base 10, a turn table 34 is disposed, and on an upper surface of the turn table 34, for example, four holding tables 30 (only two illustrated) are disposed to be spaced apart from one another at an equal interval in a circumferential direction. The turn table 34 can rotate around an axial center of a Z-axis direction on the base 10. As a result of the rotation of the turn table 34, any of the holding tables 30 are positioned close to the first transfer means 335 and the second transfer means 336.

As illustrated in FIG. 2, the holding table 30 has a circular outer shape, for example, and includes a porous plate 300 which sucks the wafer W, and a frame body 301 which supports the porous plate 300. The porous plate 300 communicates with a suction source 39 of a vacuum generation apparatus or the like, and a suction force generated as a result of suction by the suction source 39 is transmitted to a holding surface 300 a as an exposed surface of the porous plate 300, so that the holding table 30 holds the wafer W under suction on the holding surface 300 a. The holding surface 300 a is formed in a conical shape having an extremely gently inclined surface with its rotational center as an apex.

On a lower surface side of the holding table 30, holding table rotation means 37 is connected, and the holding table 30 can rotate around the axial center of the Z-axis direction by the holding table rotation means 37 on the turn table 34 illustrated in FIG. 1.

Also, an inclination adjusting mechanism 38 is disposed through a coupling or the like below the holding table 30. The inclination adjusting mechanism 38 can adjust an inclination relative to a horizontal surface of the holding surface 300 a of the holding table 30.

The holding table rotation means 37 is a pulley mechanism including a spindle 370 an axial direction of which is the Z-axis direction and an upper end of which is connected to a lower surface of the frame body 301 of the holding table 30, and a motor 371 as a driving source rotating the holding table 30 with a center of the holding table 30 as an axis for rotation. A main driving pulley 372 is mounted on a shaft of the motor 371, and an endless belt 373 is wound around the main driving pulley 372. A driven pulley 374 is mounted on the spindle 370, and the endless belt 373 is wound also around the driven pulley 374. The motor 371 rotation-drives the main driving pulley 372, and accordingly, the endless belt 373 moves rotationally in conjunction with the rotation of the main driving pulley 372. As a result, the rotational movement of the endless belt 373 rotates the driven pulley 374 and the spindle 370. For example, the motor 371 has a rotary encoder 379 connected thereto, the rotary encoder 379 detecting a rotation angle of the motor 371, that is, a rotation angle of the holding table 30.

As illustrated in FIG. 1, a column 11 is erected on a rear side of the base 10 (+X direction side). Rough-grinding feeding means 35 and finish-grinding feeding means 36 are disposed adjacent to each other on a front surface of the column 11. The rough-grinding feeding means 35 causes rough grinding means 31 to perform grinding-feeding with respect to the wafer W held on the holding table 30. The finish-grinding feeding means 36 causes finish grinding means 32 to perform grinding-feeding with respect to the wafer W held on the holding table 30.

The rough-grinding feeding means 35 includes a ball screw not illustrated, a pair of guide rails 351, a motor 352, and an elevating portion 353. The ball screw has an axial center in a vertical direction (Z-axis direction). The pair of guide rails 351 is disposed in parallel to the ball screw. The motor 352 is coupled to the ball screw and causes the ball screw to rotationally move. The elevating portion 353 has an internal nut screwed into the ball screw and has a side portion thereof in sliding contact with the guide rails 351. The motor 352 causes the ball screw to rotate, and accordingly, the elevating portion 353 supporting the rough grinding means 31 is guided with the guide rails 351 to move in the vertical direction.

The finish-grinding feeding means 36 includes a ball screw not illustrated, a pair of guide rails 361, a motor 362, and an elevating portion 363. The ball screw has an axial center in the vertical direction (Z-axis direction). The pair of guide rails 361 is disposed in parallel to the ball screw. The motor 362 is coupled to the ball screw and causes the ball screw to rotationally move. The elevating portion 363 has an internal nut screwed into the ball screw and has a side portion thereof in sliding contact with the guide rails 361. The motor 362 causes the ball screw to rotate, and accordingly, the elevating portion 363 supporting the finish grinding means 32 is guided with the guide rails 361 to move in the vertical direction.

The rough grinding means 31 includes a rotary shaft 310 whose axial direction is the vertical direction, a housing 311, a motor 312, a mount 313, and a grinding wheel 314. The housing 311 supports the rotary shaft 310 in a rotatable manner. The motor 312 rotation-drives the rotary shaft 310. The mount 313 is attached to a lower end of the rotary shaft 310. The grinding wheel 314 is detachably connected to the mount 313. A plurality of rough grinding stones 314 a in a substantially rectangular parallelepipedic shape are annularly disposed on a bottom surface of the grinding wheel 314. The rough grinding stones 314 a are formed by fixing diamond abrasive grains or the like thereto with a predetermined bonding agent. The rough grinding stones 314 a are, for example, grinding stones containing relatively larger abrasive grains.

For example, a flow passage not illustrated which communicates with a grinding water supply source and serves as a passage way for grinding water is formed within the rotary shaft 310 so as to penetrate in the axial direction of the rotary shaft 310. The flow passage opens in the bottom surface of the grinding wheel 314 so as to be able to jet the grinding water toward the rough grinding stones 314 a.

The finish grinding means 32 can perform finish grinding which enhances flatness with respect to the wafer W which is thinned through rough grinding. More specifically, the finish grinding means 32 further grinds the back surface Wb of the wafer W which has been ground by the rough grinding means 31, with a grinding wheel 314 including finish-grinding stones 324 a and rotatably mounted to the finish grinding means 32. Abrasive grains contained in the finish-grinding stones 324 a are smaller in grain diameter than the abrasive grains contained in the rough grinding stones 314 a. Configurations other than the finish-grinding stones 324 a in the finish grinding means 32 are similar to those in the rough grinding means 31.

Disposed above a moving path of the holding table 30 is cleaning means 8 cleaning the holding surface 300 a of the holding table 30. As illustrate in FIG. 2, this cleaning means 8 includes a rotary shaft 80, a housing 81, a cleaning grinding stone 82, elevating means 83. The rotary shaft 80 has an axial center in the vertical direction. The housing 81 supports the rotary shaft 80 in a rotatable manner. The cleaning grinding stone 82 is disposed at a lower end of the rotary shaft 80. The elevating means 83 causes the housing 81 to move in the vertical direction. The cleaning means 8 can be moved in a reciprocating manner in a Y-axis direction by Y-axis moving means 89 illustrated in FIG. 1.

The Y-axis moving means 89 illustrated in FIG. 1 includes, for example, a ball screw 890, a bridge portion 891, a movable portion 892, and a motor not illustrated. The ball screw 890 has an axial center in the Y-axis direction. The bridge portion 891 supports the ball screw 890. The movable portion 892 has an internal nut screwed into the ball screw 890 and moves in a reciprocating manner in the Y-axis direction on the ball screw 890. The motor is coupled to one end of the ball screw 890 and rotationally moves the ball screw 890. The cleaning means 8 is disposed on a front surface of the movable portion 892.

The cleaning grinding stone 82 is, for example, a resin bond grinding stone, or a grinding stone formed into a circular plate shape with a resin material or a ceramic material to scrape off contamination such as a grinding swarf adhered to the holding surface 300 a of the holding table 30. Incidentally, the cleaning means 8 may include a cleaning brush instead of the cleaning grinding stone 82. The elevating means 83 includes a rail 830 with which the housing 81 is in sliding motion, and a motor and the like provided inside the housing 81, for example, and causes the housing 81 to move in the vertical direction.

The grinding apparatus 1 includes imaging means 40 and a spotlight 41. The imaging means 40 illuminates the ground surface Wb of the wafer W held on the holding surface 300 a of the holding table 30 and ground with the finish-grinding stones 324 a with an illumination 400 (see FIG. 2) and images the ground surface Wb. The spotlight 41 illuminates the holding surface 300 a of the holding table 30.

The imaging means 40 is a line sensor camera, for example, and is disposed on a side surface of the housing 81 of the cleaning means 8. The imaging means 40 can move with the cleaning means 8 in the Y-axis direction and the Z-axis direction. As illustrated in FIG. 2, the imaging means 40 includes a boxlike casing 401 which blocks an external light, for example, and the illumination 400 illuminating the wafer W from above the wafer W is mounted on a side surface of the casing 401. The illumination 400 is a light emitting diode (LED) or a xenon lamp, for example, and light generated from the illumination 400 is propagated inside the casing 401 through a transmission optical system such as an optical fiber not illustrated. A light quantity of the light emitted from the illumination 400 can be adjusted by an adjuster (not illustrated) or the like.

The imaging means 40 includes a half mirror 402, an objective lens not illustrated, and an imaging portion 403. The half mirror 402 is disposed inside the casing 401 and reflects downward the light emitted from the illumination 400 to change its direction. The objective lens is disposed downstream of the half mirror 402 in the casing 401, and the reflected light on the half mirror 402 enters the objective lens. The imaging portion 403 is disposed upstream of the half mirror 402 and photoelectrically converts a reflection light reflected on the wafer W and captured by the objective lens into an electrical signal to output the electrical signal thus obtained as picture information.

The imaging portion 403 is configured such that a plurality of light receiving elements such as a charge-coupled device (CCD) are arranged side by side in a row in an X-axis direction, for example. In the imaging portion 403, a length in its longitudinal direction (X-axis direction) is substantially equal to a length of a radius of the holding surface 300 a of the holding table 30. Accordingly, the imaging portion 403 has an imaging region with a length equal to or greater than a radius of the wafer W. Data transmitted by each pixel of the light receiving elements in response to strength of the reflection light is expressed, for example, with 8-bit gradation in luminance value, namely, in 256 graduations from 0 to 255.

The spotlight 41 is an LED light or the like capable of illuminating the holding surface 300 a of the holding table 30 like a spot from above, for example, and mounted in a vicinity of the imaging means 40, more specifically, on the side surface of the housing 81 of the cleaning means 8 in the present embodiment. Note that an incident angle of a spot light from the spotlight 41 can be adjusted by adjusting means not illustrated, for example, and a diameter of the spot light can also be narrowed to a desired value. In addition, a disposition place of the spotlight 41 is also not limited to examples illustrated in FIGS. 1 and 2.

As illustrated in FIGS. 1 and 2, the grinding apparatus 1 includes control means 9 constituted by storage means 90 such as a central processing unit (CPU) and a memory and executing control of the entire apparatus. The control means 9 is electrically connected with the finish-grinding feeding means 36, the Y-axis moving means 89, the holding table rotation means 37, and the like, through wiring lines not illustrated. Under control of the control means 9, operations such as movement of the finish grinding means 32 in the Z-axis direction by the finish-grinding feeding means 36, positioning of the imaging means 40 in the Y-axis direction by the Y-axis moving means 89, and rotation of the holding table 30 by the holding table rotation means 37 are controlled. The grinding apparatus 1 further includes notification means 17 notifying the operator of various kinds of information. The notification means 17 displays the notified information on a monitor not illustrated or activates an alarm.

A description will be given below regarding operation of the grinding apparatus 1 in a case in which the wafer W is ground by the grinding apparatus 1 illustrated in FIG. 1. First, in accordance with rotation of the turn table 34 illustrated in FIG. 1, the holding table 30 with the wafer W not placed thereon revolves around the rotation axis of the turn table 34. Accordingly, the holding table 30 moves closer to the first transfer means 335. The robot 330 takes one wafer W out of the first cassette 331 to carry the wafer W onto the temporary setting table 333 a.

The positioning means 333 b centers the wafer W on the temporary setting table 333 a, and then, the detection portion 333 c detects the notch N formed at the outer peripheral edge of the wafer W. Then, the wafer W is rotated on the temporary setting table 333 a, so that the notch N is positioned at a predetermined position in the circumferential direction. Next, the first transfer means 335 causes the wafer W which has been centered and the notch N of which has been positioned at the predetermined position in the circumferential direction to be carried onto the holding table 30 so as not to displace the position of the notch N in the circumferential direction which has been grasped.

For example, the holding table 30 may include a notch alignment portion (alignment mark), not illustrated, for aligning with the notch N on the holding table 30 when the wafer W is placed on the holding table 30. On the holding table 30, the notch N of the wafer W and the notch alignment portion of the holding table 30 are aligned with each other. In other words, since the position of the notch N at the time at which the first transfer means 335 holds the wafer W has been determined when the first transfer means 335 holds and carries the wafer W from the temporary setting table 333 a, alignment is made in such a way that the holding table 30 is rotated at a predetermined angle so as to cause the position of the notch N of the wafer W which has been held on the temporary setting table 333 a and the notch alignment portion of the holding table 30 to align with each other. Thus, the wafer W is placed on the holding surface 300 a with the back surface Wb of the wafer W facing upward in such a way that the center of the holding table 30 and the center of the wafer W are substantially matched with each other.

Then, the suction source 39 (see FIG. 2) is activated to generate a suction force, and the generated suction force is transmitted to the holding surface 300 a of the porous plate 300, so that the holding table 30 holds under suction the wafer W on the holding surface 300 a. Also, the position of the notch N of the wafer W held under suction has been grasped by the control means 9.

Note that the position of the notch N of the wafer W held under suction on the holding table 30 has been constantly grasped at least until the second transfer means 336 described later transfers the wafer W from the holding table 30. More specifically, the rotary encoder 379 in the holding table rotation means 37 illustrated in FIG. 2 outputs an encoder signal (the number of rotation of the motor 371) to the control means 9 when the holding table 30 is rotated by the holding table rotation means 37. According to the received encoder signal, the control means 9 performs feedback control of a rotation speed of the holding table 30 rotated by the holding table rotation means 37, and can sequentially grasp the position of the notch N of the wafer W which is being rotated on the holding table 30.

In a case in which an edge alignment of the wafer W is carried out by use of the imaging means 40, grasping of the position of the notch N of the wafer W on the holding table 30 may be made along with the edge alignment. In the edge alignment, the holding table 30 rotates, and the outer peripheral edge of the wafer W held on the holding table 30 is imaged at a plurality of locations by the imaging means 40. Then, coordinates of three points on the outer peripheral edge of the wafer W, the three points being spaced apart from one another, are detected, for example, and an accurate center coordinate of the wafer W on the holding table 30 is obtained through geometric arithmetic processing based on the coordinates of the three points. In addition, a coordinate position of the notch N is grasped from the imaged picture obtained above.

After the holding table 30 holds under suction the wafer W, the turn table 34 illustrated in FIG. 1 rotates in a clockwise direction when it is seen from a +Z direction. As a result, the holding table 30 on which the wafer W is held revolves around the axis of the rotation of the turn table 34. Accordingly, the rotation center of the rough grinding stones 314 a of the rough grinding means 31 shifts by a predetermined distance relative to a rotation center of the wafer W, and the wafer W is positioned such that a rotation locus of the rough grinding stones 314 a passes through the rotation center of the wafer W. Moreover, the inclination of the holding table 30 is adjusted by the inclination adjusting mechanism 38 (see FIG. 2) such that the holding surface 300 a as the gently inclined conical surface becomes parallel to grinding surfaces (lower surfaces) of the rough grinding stones 314 a. Accordingly, along with the holding surface 300 a, the back surface Wb of the wafer W held under suction on the holding surface 300 a becomes parallel to the grinding surfaces of the rough grinding stones 314 a.

The rough grinding means 31 is fed in a −Z direction by the rough-grinding feeding means 35, and the rotating rough grinding stones 314 a are brought into contact with the back surface Wb of the wafer W held on the holding table 30, so that rough grinding is carried out. In addition, while the holding table rotation means 37 rotates the holding table 30 at a predetermined rotation speed, the wafer W on the holding surface 300 a is also rotated, and accordingly, the rough grinding stones 314 a carry out the rough grinding processing on the entire surface of the back surface Wb of the wafer W. During grinding, the grinding water is supplied to a contact portion between the rough grinding stones 314 a and the back surface Wb of the wafer W to cool and clean the contact portion.

After the wafer W is rough-ground close to a finished thickness, the rough-grinding feeding means 35 causes the rough grinding means 31 to move upward to be separated from the wafer W.

Next, the turn table 34 rotates in the clockwise direction when it is seen from the +Z direction, and the holding table 30 holding the wafer W under suction moves below the finish grinding means 32. After positioning between the finish-grinding stones 324 a and the wafer W is carried out, the finish grinding means 32 is fed downward by the finish-grinding feeding means 36, and the rotating finish-grinding stones 324 a are brought into contact with the back surface Wb of the wafer W. In addition, along with rotation of the holding table 30, the entire surface of the back surface Wb of the wafer W is finish-ground.

After the finish grinding means 32 grinds the back surface Wb of the wafer W to a finished thickness to thereby increase the flatness of the back surface Wb of the wafer W and is then moved away from the wafer W, the turn table 34 rotates in the clockwise direction when it is seen from the +Z direction, and as a result, the wafer W is moved closer to the second transfer means 336. Then, the second transfer means 336 transfers the wafer W on the holding table 30 to the cleaning means 334. After the wafer W is cleaned by the cleaning means 334, the robot 330 transfers the wafer W from the cleaning means 334 to load the wafer W into the second cassette 332. In the grinding apparatus 1, a series of grinding operations thus described are repeatedly performed, and a plurality of wafers W are ground.

When the wafer W is ground in the manner described above, a grinding swarf or an abrasive grain which falls off enters between the holding surface 300 a of the holding table 30 illustrated in FIG. 1 and the protective tape T attached to the wafer W illustrated in FIG. 1, and the grinding swarf or the abrasive grain may be adhered to the holding surface 300 a, in some cases. When the wafer W is ground in this state, a cross-shaped crack (cross line) is caused in the wafer W. Moreover, when a subsequent wafer W is held under suction on the holding surface 300 a with this adhered substance remained on the holding surface 300 a and the back surface Wb of the wafer W is ground, a cross-shaped crack is caused in the subsequent wafer W as well.

In view of this, the cleaning means 8 moves in the Y-axis direction by the Y-axis moving means 89 and causes the cleaning grinding stone 82 to be positioned above the holding surface 300 a of the holding table 30 from which the wafer W is transferred. Then, while the holding table rotation means 37 rotates the holding table 30, the elevating means 83 causes the cleaning grinding stone 82 which is rotating to lower and press the holding surface 300 a. As a result of the pressing, the grinding swarf or the like which protrudes from the holding surface 300 a in an upward direction is scraped off, and the holding surface 300 a is cleaned.

For example, in a case in which the plurality of wafers W are successively ground, while cleaning of the holding surface 300 a of the holding table 30 by use of the cleaning means 8 is interposed at an appropriate timing, the adhered substance may remain on the holding surface 300 a on which cleaning has been carried out by the cleaning means 8. This case results in forming the cross line on the back surface Wb of the wafer W held on the holding surface 300 a by grinding.

To prevent the formation of the cross line, it is required to prevent the plurality of wafers W from being ground with a risk of forming the cross line in the wafer W. Thus, the grinding apparatus 1 according to the present invention performs the operation described below.

For example, after the predetermined n-th wafer W (n is two or more) is ground to the finished thickness by finish-grinding and the finish grinding means 32 illustrated in FIG. 1 is separated from the wafer W, the turn table 34 rotates in the clockwise direction when it is seen from the +Z direction. Also, the Y-axis moving means 89 causes the imaging means 40 to move in the Y-axis direction, and the imaging means 40 and the wafer W are positioned such that the back surface Wb of the wafer W held under suction on the holding table 30 is imaged by the imaging means 40. More specifically, as illustrated in FIGS. 3 and 4, positioning of the imaging means 40 and the wafer W is performed such that the imaging portion 403 extends in a line shape between an upper side of a center We of the wafer W and an upper side of the outer peripheral edge of the wafer W. Note that, in FIGS. 3 and 4, configurations other than the imaging portion 403 in the imaging means 40 are omitted.

Next, the holding table rotation means 37 rotates the holding table 30 by a predetermined angle under control of the control means 9, and for example, as illustrated in FIG. 4, a virtual line L1 passing through the center We of the wafer W and the notch N is parallel to the X-axis direction, and the notch N is positioned at a position on the +X direction side (at a 0-degree position serving as an imaging start position).

Also, the imaging means 40 is operated, and focusing of the objective lens not illustrated is performed in accordance with vertical movement of the imaging means 40 by the elevating means 83 illustrated in FIG. 2. At the time point at which the objective lens focuses on the back surface Wb of the wafer W, the elevating means 83 stops the vertical movement of the imaging means 40.

In this state, as illustrated in FIGS. 3 and 4, the holding table rotation means 37 rotates the holding table 30 at a predetermined rotation speed in a counterclockwise direction when it is seen from the +Z direction, for example. Also, the illumination 400 of the imaging means 40 (see FIG. 2) irradiates the back surface Wb of the wafer W with light through the half mirror 402, and a reflected light from the back surface Wb of the wafer W is captured by the objective lens not illustrated and transmitted through the half mirror 402 to enter a light receiving element in the imaging portion 403. Then, the back surface Wb of the wafer W which relatively rotates relative to the imaging means 40 is successively imaged line by line from the center We of the wafer W to its outer peripheral edge by the imaging means 40.

The imaging portion 403 sequentially sends the imaged pictures in units of line to the control means 9 illustrated in FIGS. 1 and 2. The imaged pictures in units of line are stored in the storage means 90 in the control means 9 in order such that an imaged picture on which the entire back surface Wb of the wafer W is imaged can be configured. In addition, according to the encoder signal received by the rotary encoder 379 (see FIG. 2) in the holding table rotation means 37 which rotates the holding table 30, the control means 9 associates an imaged picture indicating one line on the back surface Wb of the wafer W with a rotation angle of the holding table 30 from the imaging start position (0-degree position) when the imaged picture indicating the one line is imaged to store the imaged pictures in order in the storage means 90.

When the holding table rotation means 37 rotates the holding table 30 at 360 degrees and the imaging means 40 has made one round above the back surface Wb of the wafer W (the notch N is returned to the imaging start position), an imaged picture on which the entire surface of the back surface Wb of the wafer W is imaged is formed. In addition, the rotation of the holding table 30 is stopped.

A light quantity (light receiving quantity) of the reflected light which has entered each of the light receiving elements in the imaging portion 403 causes a difference in a case in which the cross line is present on the back surface Wb of the wafer W. In other words, in each of the light receiving elements in the imaging portion 403, the light receiving quantity increases on a portion of the back surface Wb of the wafer W with the cross line, and its luminance value approaches 255 and becomes closer to white. On the other hand, the light receiving quantity decreases in a region in which the cross line is not present on the back surface Wb of the wafer W, and its luminance value approaches 0 and becomes closer to black. Accordingly, in an imaged picture G reflecting the entire surface of the back surface Wb of the wafer W which is displayed on a virtual output screen with a predetermined resolution illustrated in FIG. 5, a cross line C on the back surface Wb of the wafer W is indicated in white, for example, and the back surface Wb of the wafer W around the cross line C is indicated in gray.

Incidentally, binarization processing may be executed on the imaged picture G, so that the cross line C and the periphery thereof can be clearly distinguished from each other.

As illustrated in FIGS. 1 and 2, the grinding apparatus 1 includes detecting means 91 detecting the cross line C in the imaged picture G imaged by the imaging means 40. The detecting means 91 is incorporated in the control means 9, for example. The detecting means 91 counts a sum of white pixels in the Y-axis direction and a sum of white pixels in the X-axis direction in the back surface Wb of the wafer W (in a gray region) imaged on the imaged picture G indicated in FIG. 5, to thereby detect the cross line C and calculate a size of the cross line C. In addition, a pixel at an intersection point of the cross line C is identified.

Next, an X-axis and Y-axis coordinate position of the pixel at the intersection point of the cross line C thus detected is determined by the detecting means 91. A coordinate position of the center We of the wafer W which substantially matches with a rotation center of the holding table 30 is set as an origin coordinate (0, 0), for example, and a virtual line L2 connecting the origin coordinate (0, 0) and the intersection point of the cross line C which has been identified is drawn. An angle θ1 between the virtual line L1 and the virtual line L2 is identical to an angle at which the holding table 30 rotates from the imaging start position when the imaged pictures in units of line with the cross line C imaged thereon are imaged, and is a known value which has been preliminarily stored in the storage means 90.

Also, a length of the virtual line L2 is calculated by counting pixels from the origin coordinate (0, 0) to the pixel at the intersection point of the cross line C (assuming the calculated value is r, for example). Thus, the X-axis and Y-axis coordinate position (x, y) of the pixel at the intersection point of the cross line C detected is determined to be (r cos θ1, −r sin θ1). Then, the X-axis and Y-axis coordinate position at the intersection point of the cross line C, (r cos θ1, −r sin θ1), is stored in the storage means 90.

Note that the determination of the X-axis and Y-axis coordinate position (x, y) of the pixel at the intersection point of the cross line C detected is not limited to the example described above. For example, a virtual line L3 (not illustrated in FIG. 5) which is orthogonal to the virtual line L1 is drawn from the pixel at the intersection point of the cross line C, and an X-axis coordinate of an intersection point between the virtual line L1 and the virtual line L3 is determined by counting the pixels from the origin coordinate (0, 0) to the intersection point between the virtual line L1 and the virtual line L3. Then, by further counting the pixels from the intersection point between the virtual line L1 and the virtual line L3 to the intersection point of the cross line C, a Y-axis coordinate position of the intersection point of the cross line C is determined, and accordingly, the X-axis and Y-axis coordinate position (x, y) of the intersection point of the cross line C may be finally determined.

When the X-axis and Y-axis coordinate position at the intersection point of the cross line C, (r cos θ1, −r sin θ1), is stored in the storage means 90, the stored X-axis and Y-axis coordinate position (r cos θ1, −r sin θ1) on the back surface Wb of the wafer W is illuminated with the spotlight 41 illustrated in FIGS. 1 and 2. More specifically, under control of the control means 9, movement of the spotlight 41 in the Y-axis direction by the Y-axis moving means 89, movement of the spotlight 41 in the Z-axis direction by the elevating means 83, and/or adjustment of an incident angle of the spot light irradiated from the spotlight 41 by the adjusting means not illustrated are carried out, so that the spotlight 41 illuminates the stored X-axis and Y-axis coordinate position (r cos θ1, −r sin θ1) on the back surface Wb of the wafer W at a predetermined spot diameter. Note that the spot diameter of the spot light from the spotlight 41 is, for example, a diameter having a size of longitudinal and lateral lengths of the cross line C.

As described above, when the detecting means 91 detects the cross line C, the control means 9 sends the control signal to the notification means 17, and the notification means 17 notifies the operator that the cross line C has been detected on the wafer W. Further, under control of the control means 9, grinding operations, specifically, transferring the wafer W by the first transfer means 335 to a holding table 30 other than the holding table 30 holding the wafer W in which the cross line C has been formed, rough grinding processing (finish-grinding processing) on the wafers W held on another holding table 30, transferring the wafer W in which the cross line C has been formed from the holding table 30 to the cleaning means 334 by the second transfer means 336, rotating the turn table 34, and the like are stopped. As a result, the operator removes the wafer W in which the cross line C has been formed from the holding table 30, and thereafter, the grinding apparatus 1 is in a state in which the adhered substance on the holding surface 300 a of the holding table 30 can be removed.

Incidentally, in a case in which the cross line C is not detected on the wafer W, similarly as described above, rotation of the turn table 34 moves the wafer W closer to the second transfer means 336, and the second transfer means 336 transfers the wafer W on the holding table 30 to the cleaning means 334.

After the grinding operations in the grinding apparatus 1 are stopped as described above, suction of the wafer W with the cross line C detected thereon by the holding table 30 is cancelled, and the wafer W is no longer held on the holding table 30 to thereby be transferred from the holding table 30 by the operator, as a wafer unsuitable for a product wafer. Accordingly, the spotlight 41 (see FIG. 2) illuminating the stored X-axis and Y-axis coordinate position (r cos θ1, −r sin θ1) on the back surface Wb of the wafer W at a predetermined spot diameter results in illuminating the holding surface 300 a directly below the X-axis and Y-axis coordinate position (r cos θ1, −r sin θ1) where the cross line C has been formed in the wafer W with the spot light. In other words, the adhered substance on the holding surface 300 a which has caused formation of the cross line C is in a state of being illuminated by the spotlight 41 in a pinpoint manner.

The operator can immediately grasp the position where the minute substance such as a grinding swarf and an abrasive grain is adhered onto the holding surface 300 a with the spot light emitted from the spotlight 41. Hence, the operator can instantly remove the adhered substance which causes the cross line C from the holding surface 300 a, for example, by use of a tool for removing the adhered substances (a scraper or a cleaning brush, for example).

After removal of the adhered substance from the holding surface 300 a by the operator is performed as described above, the operator sets the grinding apparatus 1 such that the grinding operations of the grinding apparatus 1 can be started again. Then, the wafer W is held on the holding table 30 which turns into the holding surface 300 a in a state in which the cross line C is not formed in the subsequent wafer W, and the grinding operations are performed.

Note that the grinding apparatus 1 according to the present invention is not limited to the embodiment described above, and the configurations and the like in each of the apparatuses illustrated in the attached drawings are also not limited thereto. Various modifications and alterations can be made within the scope exerting the effects of the present invention.

For example, the spotlight 41 may start to illuminate the X-axis and Y-axis coordinate position at the intersection point of the cross line C, (r cos θ1, −r sin θ1), which is stored in the storage means 90, after the operator transfers the wafer W in which the cross line C is detected, from the holding table 30.

The present invention is not limited to the details of the above described preferred embodiment. The scope of the invention is defined by the appended claim and all changes and modifications as fall within the equivalence of the scope of the claim are therefore to be embraced by the invention. 

What is claimed is:
 1. A grinding apparatus comprising: a holding table including a porous plate having a holding surface on which a wafer is held; holding table rotation means rotating the holding table with a center of the holding table as an axis for rotation; grinding means grinding the wafer held on the holding surface with grinding stones; notification means notifying an operator of various kinds of information; imaging means illuminating a ground surface of the wafer which is held on the holding surface and ground with the grinding stones with an illumination and imaging the ground surface; detecting means detecting a cross line in a picture imaged by the imaging means; storage means storing an X-axis and Y-axis coordinate position of an intersection point of the cross line detected by the detecting means; a spotlight illuminating the holding surface at the X-axis and Y-axis coordinate position stored in the storage means; and control means causing the notification means to notify the operator that the detecting means has detected the cross line and stopping grinding operations of the grinding apparatus. 